This invention relates primarily to the field of imaging and, more specifically, to an apparatus for the combined use of ultrasound and near infrared diffused light imaging.
Ultrasound imaging is a well-developed medical diagnostic that is used extensively for differentiation of cysts from solid lesions in breast examinations, and it is routinely used in conjunction with mammography to differentiate simple cysts from solid lesions. Ultrasound can detect breast lesions that are a few millimeters in size; however, its specificity in breast cancer detection is not high as a result of the overlapping characteristics of benign and malignant lesions. The sonography appearance of benign and malignant lesions have considerable overlapping features, which has prompted many radiologists to recommend biopsies on most solid nodules. Thus, the insufficient specificity provided by ultrasound results in a large number of biopsies yielding benign breast masses or benign breast tissue (currently 70 to 80 percent of biopsies yield benign changes).
Recently, optical diagnostics, based on diffusing near infrared (NIR) light, have been employed in breast cancer detection. Functional imaging with NIR light is made possible in a spectrum window that exists within tissues in the 700-900 nm NIR region, in which photon transport is dominated by scattering rather than absorption. Functional imaging with NIR light offers several tissue parameters to differentiate tumors from normal breast tissue. For example, functional imaging with NIR light has the potential to differentiate tumors from normal breast tissue through determination of blood volume, blood O.sub.2 saturation, tissue light scattering, water concentration, and the concentration and lifetime of exogenous contrast agents.
While NIR imaging has the potential to improve tumor specificity, its relatively low resolution makes it unsuitable for morphological diagnosis. Its resolution is intrinsically limited by the diffusive nature of NIR light in tissue. Currently, typical NIR imaging instruments can distinguish simple structures approximately 1 centimeter in size; however, sharp edges are typically blurred by a few millimeters. Unfortunately, the relatively poor resolution of the optical reconstruction makes it difficult to take full advantage of the improved tumor specificity that would otherwise be provided by NIR imaging.